<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div>
        <script>
            a = 5;
            b = 6;
            c = a + b;
            console.log('---->', c);
            alert(c)
        </script>
    </div>
    <div>
        <script>
            var x = 15 * 5;
            debugger;
            document.getElementById("demo").innerHTML = x;
        </script>
    </div>
</body>

</html>